Store image to Blobstore from android client and retrieve blobkey and upload url to store in Datastore. - GAE

Question

In my Android application, I want to upload image to the Blobstore, then retrieve an Upload url and the image\'s Blobkey, so I can store the Blobkey in the DataStore.

Answer 1

After many tries i solved this problem. To store image in blobstore, first android needs to make request to servlet which will generate upload url :

Android client : It will request to generate url and gets url from servlet

HttpClient httpClient = new DefaultHttpClient();    
//This will invoke "ImgUpload servlet           
HttpGet httpGet = new HttpGet("my-app-url/ImgUpload"); 
HttpResponse response = httpClient.execute(httpGet);
HttpEntity urlEntity = response.getEntity();
InputStream in = urlEntity.getContent();
String str = "";
while (true) {
    int ch = in.read();
    if (ch == -1)
        break;
    str += (char) ch;
}

ImgUpload.java - Servlet to generate url and sends response to client

BlobstoreService blobstoreService = BlobstoreServiceFactory
            .getBlobstoreService();
public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {

//"uploaded" is another servlet which will send UploadUrl and blobkey to android client
String blobUploadUrl = blobstoreService.createUploadUrl("/uploaded"); 

        resp.setStatus(HttpServletResponse.SC_OK);
        resp.setContentType("text/plain");

        PrintWriter out = resp.getWriter();
        out.print(blobUploadUrl);
    }

In android client,write below code upload image to returned response from above servlet.

//Save image to generated url
HttpPost httppost = new HttpPost(str);
File f = new File(imagePath);
FileBody fileBody = new FileBody(f);
MultipartEntity reqEntity = new MultipartEntity();
reqEntity.addPart("file", fileBody);
httppost.setEntity(reqEntity);
response = httpClient.execute(httppost); //Here "uploaded" servlet is automatically       invoked
urlEntity = response.getEntity(); //Response will be returned by "uploaded" servlet in JSON format
in = urlEntity.getContent();
str = "";
while (true) {
    int ch = in.read();
    if (ch == -1)
        break;
    str += (char) ch;
}
JSONObject resultJson = new JSONObject(str);
String blobKey = resultJson.getString("blobKey");
String servingUrl = resultJson.getString("servingUrl");

uploaded.java- servlet which returns Uploadurl and Blobkey of image

BlobstoreService blobstoreService = BlobstoreServiceFactory
            .getBlobstoreService();

    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        try {
            List blobs = blobstoreService.getUploads(req).get("file");
            BlobKey blobKey = blobs.get(0);

            ImagesService imagesService = ImagesServiceFactory
                    .getImagesService();
            ServingUrlOptions servingOptions = ServingUrlOptions.Builder
                    .withBlobKey(blobKey);

            String servingUrl = imagesService.getServingUrl(servingOptions);

            resp.setStatus(HttpServletResponse.SC_OK);
            resp.setContentType("application/json");

            JSONObject json = new JSONObject();

            json.put("servingUrl", servingUrl);
            json.put("blobKey", blobKey.getKeyString());

            PrintWriter out = resp.getWriter();
            out.print(json.toString());
            out.flush();
            out.close();
        } catch (JSONException e) {

            e.printStackTrace();
        }

    }